Editing/Changing an Existing Mail Merge Spreadsheet

You will want to be in Step 3 Customize: 

• On the right-hand side click on Object List
• Locate the Text Object that has your merged data and use the Trash Can Icon to delete that text box

• Then go back to the left-hand side and select Import Data
• Select Replace Spreadsheet

• Finally, select Browse for File to import your new Spreadsheet

 To learn more about this, watch this video: